Author Topic: 1/3rd scale V10  (Read 219248 times)

Offline BillTodd

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Re: 1/3rd scale V10
« Reply #165 on: July 24, 2015, 03:19:01 PM »
Fan- bloody -tastic :-)
Bill
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Online Vixen

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Re: 1/3rd scale V10
« Reply #166 on: July 24, 2015, 03:40:53 PM »
Hello Keith

I have the same problem with the supercharger rotors for the 1:3 scale Mercedes W165 engine I am building. I have started a build log but that is running about 1 year behind actual progress.

My rotors are much simpler than yours. I have two lobe rotors, straight and without the twist. The W165 has a two stage supercharger (I prefer the German word: Kompressor) which requires two different rotor sets; a short, high pressure and a longer low pressure rotor. Both have identical cross sections, only the length is different.

As you have discovered, it is the backlash in the synchronising gears which causes all the trouble and allows the flanks of the rotors to touch. Idealy the rotor clearance needs to be within a few thou to prevent pressure leakage. In the home workshop we are never likely to make make our synchronising gears to that sort of precision without specialist gear honing equipment.

When I assembled my rotors, I found they touched in several places. They would rotate, but they touched. All the high spots were hand scraped and more would appear in different places when the rotors were reassembled. So pull them apart, remove the high spots, reassemble and repeat the process indefinitely. Contact was occurring on both the leading and trailing faces of the rotors and was entirely due to the backlash in the synchronising gears. It also became abundantly clear that each rotor and each gear and even each woodruff key had to be kept together as matched sets, otherwise you start all over again.

In the end I decided it was much more sensible to have generous clearance between the rotors which would also allow for some wear in the gears as they bedded in. Besides did I really want 39 psi boost pressure on model engine running on the bench? So what, if the Kompressors leak and do not make maximum pressure, it is far more important that they continue to rotate reliably. If nothing else, they will act as blenders to keep the fuel and air well mixed.

Good luck

Mike
« Last Edit: July 24, 2015, 03:56:57 PM by Vixen »
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Offline billmac

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Re: 1/3rd scale V10
« Reply #167 on: July 24, 2015, 04:36:54 PM »
This just keeps getting better and better. Sorry to hear about the small problem with the rotors, but I am sure you will work around that. Please keep us up to date; I look forward to seeing the latest progress reports.


Offline Greg Haisley

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Re: 1/3rd scale V10
« Reply #168 on: July 24, 2015, 08:11:30 PM »
Well, I'm still here. Seems I'm not much of a poster, or photographer, but I have a few pics to bring me up to date.

I made the housing for the supercharger rotors, and the gearbox housing, and then ran the rotors together with the helical gears fitted.
there was loads of interference with the rotors, so I just ran it for a bit and then removed the contact spots, and then ran it again.
This time it contacted somewhere else, so I removed those points.

Anyway, I went through this rigmarole about 12 times and they were still catching. It turns out that even though I'd closed the theoretical centrelines of the gears up a couple of thou' there was still too much backlash between the gears to keep the rotors where they should be.
there is about 4 thou' movement at the rotor tips. This needs to be 1 thou' at a guess. I ordered some gears with slightly longer centerline and I'm going to mesh them together with grinding paste, to get almost zero backlash at the centres I'm now stuck with.

Sorry for brief explanations, I don't get long for lunch here.

Maybe I can help you with the clearance problem. Replacing the loose gears is a must. The gears need to run minimum clearance like you said maybe a .001 or so.

  On a GMC blower the driven rotor has a splined shaft pinned into the driven rotor. The gear has to have a splined bore to match the splined shaft. This shaft allows the helical gear to move back and forth. The driven gear may be shimmed to twist this rotor independently from the driving gear to create tighter or looser rotor clearance because of the helix angle. The driving gear also has to be bolted to the rotor, preferably just like the driven gear (splined shaft pinned to the rotor). I'd start out with .010 shim stock between the driven gear and rotor, with both rotors lined up, then pin the driven rotor to the splined shaft. Now you can adjust the backlash between the rotors by adding or subtracting shims from behind the driven gear to suit the clearance you are looking for.  A street blower runs around .004 to .006 clearance at the edge to edge of the rotors.

Good luck Keith
Cheers,
Greg Haisley

Online Vixen

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Re: 1/3rd scale V10
« Reply #169 on: July 24, 2015, 08:45:13 PM »

  A street blower runs around .004 to .006 clearance at the edge to edge of the rotors.


That amount of clearance sounds very practical, sensible and generous rotor clearance

Mike
« Last Edit: July 24, 2015, 09:42:59 PM by Vixen »
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Offline dr_kingston

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Re: 1/3rd scale V10
« Reply #170 on: July 29, 2015, 08:19:03 AM »
Hi Keith,
I built a Commer knocker type blower years ago and to overcome the sync gear backlash problem the non drive rotor shaft had 2 gears fitted. (one was 1/3d the width of the other).
The narrow gear had clearance on the bolt holes that allowed for adjustment to take out the backlash. (Zero backlash clearance is possible at start up). 
It worked for me.
Regards Dale

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Re: 1/3rd scale V10
« Reply #171 on: July 29, 2015, 12:33:53 PM »
Dale,
That sounds like an excellent idea to eliminate the synchro gear backlash. I assume the 2/3 wide gear face is the one that does all the work and the 1/3 wide face does not transmit power, it only looks after the backlash.
I will look to see how that modification can be applied to my 1:3 scale Mercedes W165 two stage blowers.
Mike

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Offline jschoenly

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Re: 1/3rd scale V10
« Reply #172 on: July 29, 2015, 12:44:29 PM »
Man, that is just an awesome bit of design and machining there. 

I can't remember/find if I asked previously, but why the slightly offset crank pins on the throws?  Never saw that before and just curious.  Beautiful work!
Jared
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Offline DavidF

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Re: 1/3rd scale V10
« Reply #173 on: July 29, 2015, 02:49:57 PM »
Ive been looking at supercharger rotors and how they mesh and thinking about the backlash of the gears.  What im thinking is that if the rotor profiles are modeled with a cycloidal profile then it should keep the rotors from colliding even if there is some lash in the gears?? Im hoping one day to make a full scale supercharger for my flathead build. :insane:

Offline Admiral_dk

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Re: 1/3rd scale V10
« Reply #174 on: July 29, 2015, 11:17:08 PM »
I know that Honda has used the same idea of an extra gear next to the one doing the work and the extra gear is pre-tightened with a spring - used on their gear-driven camshafts => zero backlash  :old:

http://smg.photobucket.com/user/lateott_156/media/CB-1Story/06.jpg.html

Offline dr_kingston

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Re: 1/3rd scale V10
« Reply #175 on: July 29, 2015, 11:29:00 PM »
Hi Mike,
This type of backlash reduction works a treat. Yes 2/3 gear face does the driving. The 1/3 and 2/3 gears were bolted together as a complete unit and the teeth were cut on a hobber as one gear.
The gears were mated together with no spring loading for the backlash removal.
Regards Dale

Offline keith5700

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Re: 1/3rd scale V10
« Reply #176 on: July 30, 2015, 08:01:24 AM »
Thanks for comments/suggestions. I've got a few other projects on at the minute, so progress is slow on the V10.
I think the gears I am fitting now should have pretty much zero backlash when run in with a bit of paste.
I guessed at about 4 thou' backlash at the rotor tips, but I rigged a clock up the other day and it is 10 thou'!
This includes reducing the gear manufacturers recommended centres slightly.

Hopefully these gears will sort the problem.

Jared, the offset crank pin is there so I can have an 82 degree vee block instead of a 72 degree vee, and still have an even fire engine.
The crank offset is 10 degrees, which effectively delays the firing on the second bank by the same amount.

The wider vee gives me more space to get the intake/supercharger stuff in.
Cheers.

Offline jschoenly

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Re: 1/3rd scale V10
« Reply #177 on: July 30, 2015, 01:38:41 PM »
Innovative!  Thanks, I had been wondering.  Keep up the awesome work, at whatever pace available!  ;)
Jared
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Offline keith5700

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Re: 1/3rd scale V10
« Reply #178 on: August 20, 2015, 12:45:46 PM »
I've just had a week off work so I had a target to make the oil pump during the week.
I tried to remember to take photos this time too.
The pump is a 3 stage affair, with 2 x scavenge sections and 1 x pressure section, at the rear.
I've had the gears ready for a while.

there are ptfe gaskets between each face, which should seal the sections and provide a nice face for the gears to rub on.

I had to grind a 1/16" woodruff cutter down to 1.2mm, for the keyways in the shaft.

pump is now just about complete and ready for anodising over the weekend, if I can decide on the color scheme!






















Online Vixen

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Re: 1/3rd scale V10
« Reply #179 on: August 20, 2015, 05:34:54 PM »
Keith
I like the idea of the ptfe gaskets between each section to seal the pump sections and to provide a nice face for the gears to rub on, but is there a risk of the gears ripping up the ptfe gasket? My Mercedes W165 is over the top with the internal oil pumps, thee pressure and four scavenge and then a separate external scavenge pump just for the blowers

What diameter is the driven shaft and what is the size of the gears?

Regards

Mike
It is the journey that matters, not the destination